The present invention relates generally to the control and governing of aircraft propeller blade pitch, and more specifically, to a method and apparatus for a self-contained variable pitch and/or constant speed propeller including provisions for feathering and reverse pitch operation. The invention is further applicable to marine propellers, windmills, and axial impellers for ventilation and other air handling applications such as wind tunnels. Briefly, the present invention provides a method and apparatus contained within an aircraft propeller that enables adjustment of the propeller blade pitch setting to a selected angle, or the maintenance of a selected rotational velocity via adjustment of blade pitch.
The advantages of an in flight controllable pitch propeller have been well known since early twentieth century. As such, there have been many systems developed for controlling aircraft propeller blade pitch. Most such systems have in common at least the following three requirements: (1) the current operating conditions of the propeller must be known to the systemxe2x80x94for a controllable pitch system, this would be the current blade pitch setting, whereas for a constant speed system utilizing a governor, this would be the current angular velocity and the angular acceleration, or some function thereof; (2) the desired propeller operating conditions must be knownxe2x80x94this would be the selected blade pitch setting for a variable pitch unit, or the selected angular velocity for a constant speed unit; and (3) some form of power must be available to operate the blade pitch change mechanism.
One of the most successful propeller blade pitch changing systems has been the hydraulic system, originally developed by Hamilton Standard, wherein the hydraulic system routes oil pressure from the aircraft engine, or gearbox, through the propeller shaft to provide a means for changing blade pitch. The oil pressure in the propeller shaft is controlled by a governor, which in turn, adjusts the blade pitch to maintain a selected engine rotation speed.
Other methods and systems include various electric systems, wherein electrical power to control the blade pitch is sourced from the aircraft electrical system and transferred to the propeller by means of slip rings or brushes. Mechanical systems for controlling blade pitch have also been utilized, wherein a bearing ring is utilized to transfer motion from a device mounted on the airframe to the propeller for blade pitch changing purposes.
All of the previous systems, however, share the same disadvantage; they problematically depend upon having to transfer the requisite power for blade pitch change from a fixed portion of the engine, or airframe, to the rotating propeller, thus making propeller installation significantly more complex. Specifically, the hydraulic system requires an oil passage through the propeller shaft to the propeller and associated blades, wherein the oil pressure within the propeller shaft must be regulated, and in some cases boosted, by a governor attached to the engine or gearbox. Typically, the governor requires its own set of oil passages, as well as the appropriate mounting pad and drive, thus further complicating, propeller installation. Additionally, hydraulic systems must be effectively sealed to prevent loss of propeller control or even worse, loss of engine or gearbox oil, and therefore, require frequent maintenance for preservation of the system.
With regard to electrical systems, the slip rings or brushes utilized for transferring power to the propeller require frequent replacement and adjustment, are generally unduly expensive, and therefore increase overall maintenance costs. Furthermore, for systems integrity and operational capacity, such electrical systems must be well shielded from electrostatic and/or electrical environmental implements, such as lightning, and/or from other sources of electrical disturbance.
Although relatively structurally simple, mechanical systems are often difficult to implement without incurring significant weight and maintenance problems. In particular, the operational nature of the rotating-to-fixed bearing assembly, utilized for transferring mechanical motion from the engine or airframe to the propeller, generally calls for frequent maintenance, and therefore overrides any benefit otherwise derived from the simplistic installation and design of such a system.
Essentially, in addition to the aforementioned deficiencies, disadvantages and impracticalities, the above-discussed blade pitch changing systems suffer, in general, from added complexity, maintenance requirements, and safety of flight issues, as functional operation of each system burdensomely requires that the blade pitch setting information and the requisite power to change such blade pitch be transferred hydraulically, electrically or mechanically from the fixed engine or airframe to the rotating propeller, thus overly complicating propeller installation.
Therefore, it is readily apparent that there is a need for a self-contained variable pitch and/or constant speed propeller that requires no direct contact of any type, hydraulic, pneumatic, electrical, or mechanical, between the fixed engine or airframe and the rotating propeller, thus facilitating propeller installation and reducing overall system maintenance.
Briefly described, in a preferred embodiment, the present invention overcomes the above-mentioned disadvantages and meets the recognized need for such a device by providing, a method and apparatus for a self-contained variable, pitch and/or constant speed propeller including provisions for feathering and reverse pitch operation, wherein no direct contact is required between the fixed engine or airframe and the rotating propeller for effectuation of blade pitch change, therefore eliminating the burdens and complexities generally associated with propeller installation, maintenance and blade pitch change operations.
According to its major aspects and broadly stated, the present invention in its preferred form is a method and apparatus for a self-contained variable pitch and/or constant speed propeller including provisions for feathering and reverse pitch operation, having, in general, a blade control module, command module, power module, and pitch changer, functioning in association with a propeller hub, propeller blades and propeller shaft housing.
More specifically, in the preferred form, power is supplied by a simple permanent magnet alternator arranged such that the magnets are attached to the fixed portion of the engine, gearbox, or airframe and the coils are attached to the propeller hub. The power available from the alternator can be varied by the number and radial location of the coils and magnets utilized. The necessary power for a specific propeller must be sufficient to change the blade pitch at the maximum required rate when operating at a relatively low angular velocity. The required power available from the alternator will be a function of the specific propeller design. The current flow induced in the coils by the rotation of the propeller goes to a conventional power control module in the propeller hub which provides controlled voltage D.C. power available to operate the system. The pitch setting information is supplied by two non-contact position sensors arranged as follows: (1) the detector halves of the sensors are attached to the rotatable propeller hub along a single radial or azimuth, wherein the other portions of the sensors are attached to the fixed airframe or engine; and wherein (2) one of the sensor halves on the fixed airframe or engine serves as the reference sensor, and is not adjustable. The other sensor half on the fixed airframe or engine is adjustable azimuthally and serves as the command sensor.
The signals from the sensors go to the blade control module, an integrated circuit device with simple computing and timing capability.
The output from the sensors is used to determine the current angular velocity, angular acceleration, and the position of the adjustable sensor relative to the reference sensor. The time for each revolution is measured using the reference sensor signals. The mean angular velocity for each revolution is simply the inverse of the time intervalxe2x80x94if the time is measured in seconds, then the angular velocity is in revolutions per second. The angular acceleration is determined by obtaining the difference in angular velocity of successive revolutions and dividing it by the difference in time of the same successive revolutions. The position of the command sensor is determined by the ratio of the time from the beginning of a revolution to passage of the command sensor to the time for the complete revolution. When the angular velocity is constant, this ratio gives the position exactly. When an angular acceleration is present, a correction to the measured position is required to eliminate substantial errors in the calculated position. One method of correction is to correct the time measured from the beginning of the revolution to command sensor passage for the acceleration. Using the time between adjustable sensor passages, the mean angular velocity of the command sensor is determined. A simple algebraic function using the ratio of the command sensor angular velocity to the reference sensor angular velocity is then employed to correct the measured time between reference and command sensor passage for angular acceleration. The ratio of this corrected time to the time for the revolution is then used to determine the adjustable sensor position. This reduces the error in adjustable sensor position determination to well under one percent, except for cases where the angular acceleration is very large and the angular velocity is very small, such as when the engine is starting or is just stopping. Exact knowledge of the command sensor position is not necessary at those conditions.
An alternative method of determining the angular velocity and acceleration is readily available from the alternator. The frequency of the A.C. alternator output may be analyzed to determine angular velocity, wherein the change of frequency with time can provide the angular acceleration. There may be some applications where this approach would be advantageous. Since both the reference and command non-contact sensors are still required, this approach adds a layer of complexity, and for that reason is only an alternative method.
The selected propeller operating condition is determined as a function of the command sensor position. Since the command sensor position is a direct function of the ratio of acceleration corrected time for command sensor passage to time for the current revolution, it is convenient to use this ratio in lieu of the actual angular position of the command sensor relative to the reference sensor. In its simplest and preferred form, the function is merely an appropriate constant determined by the placement and motion range of the command sensor, multiplied by the aforementioned time ratio. The result of that multiplication can be the selected pitch angle for variable pitch operation, or the selected angular velocity for constant speed operation.
The blade control module performs the necessary calculations as described above and uses several logical tests to determine the output to the pitch changer. The logical tests will be different depending upon whether the operation is variable pitch or constant speed. For variable pitch operation, the pitch changer is driven to position the blades at the selected pitch angle. Both constant speed and variable pitch operation require a feedback sensor using the position of the pitch changer or the pitch change mechanism to define the current pitch angle of the blade. Constant speed operation is slightly more complex in that the pitch changer must be operated in a manner that achieves the selected angular velocity with a minimum of hunting, overshoot, and undershoot. The basic logic for constant speed operation pitch change is quite simple; if the measured angular velocity is less than the selected velocity, blade pitch is decreased, if greater, blade pitch is increased. Since the exact blade pitch setting for the selected angular velocity is never known and constantly varies as the aircraft maneuvers, the blade control module contains logic which uses the current and selected angular velocities and the angular acceleration to adjust the blade pitch in a manner that will minimize hunting, overshoot, and undershoot. A preferred form of the logic utilizes a nominal angular acceleration based on the difference between the current angular velocity and the selected angular velocity. For example, when angular velocity is less than the selected angular velocity and the angular acceleration is positive, the blade pitch would be increased if the angular acceleration is greater than nominal, or would remain the same if the angular acceleration was nominal, or would be decreased if the angular acceleration was less than nominal. A reference angular acceleration, defined as the difference between actual and nominal angular accelerations, is utilized to define the pitch change rate.
The blade control module output controls the direction and rate of motion of the pitch changer. The term xe2x80x9cpitch changerxe2x80x9d as used herein refers to a device that provides the force and motion to the pitch change mechanism to change the blade pitch. There are many types of pitch changers that may be utilized, ranging from electrical stepper motors, electrical linear actuators, to electro hydraulic units and electro pneumatic units. The type used will depend on the system being designed and will be influenced by the type of pitch change mechanism selected for the individual propeller design. Whatever type is utilized, however, it must meet the following requirements: (1) it must be electrically driven; (2) it must be reversible; (3) the rate at which it operates must be variable; and, (4) it must be sufficiently powerful to produce the maximum pitch change rate required for the specific propeller. In a preferred embodiment, the pitch changer would be a variable speed reversible electric motor, and the pitch change mechanism would be a beveled gear turned by the pitch changer and engaging beveled gears on the propeller blade roots to rotate the blades and, accordingly, change the blade pitch.
The present invention is suitable for many applications. Specifically, some airplanes require additional capability. Multi-engine airplanes and powered sailplanes, for example, require propellers that can be feathered if an engine is shut down. Some airplanes further require reverse thrust capability which requires reverse pitch settings. As such, feathering capability is obtained by the following additions to the basic system for constant speed or variable pitch operation: (1) a blade pitch position sensor that can be utilized to determine that the blades are in the feathered position, wherein the blade position is fed back to the blade control module; (2) the feather command is accomplished by a gate protected extended travel capability for the, command sensor (alternatively, an additional non-contact feather sensor that is activated by the selection of the feather condition may be utilized instead), wherein selection of feather can be either by a cockpit command or from the auto feather command in cases where auto-feather is required; (3) the blade control module would possess additional logic to determine the state of the command sensor or the feather sensor, wherein if either sensor is in the feather position, the blade control module activates the pitch changer to move the blades to the feather position; (4) a device for storing energy is required to ensure the completion of the feathering operation and to facilitate unfeathering, wherein the alternator would provide power for moving the blades only when the propeller is rotating, and wherein additional logic would be added to the blade control module to use power from the stored energy source (i.e., an electrical storage battery) when the alternator is not operating or is not producing sufficient power; and, (5) provision for a charging device to use power from the alternator to maintain the energy storage device in a fully charged condition during normal operation.
Unfeathering capability is equally important and in a preferred embodiment would be accomplished in the following manner: (1) the command sensor is placed in the normal operating range, or the feather sensor is deactivated and the starter is engaged to initiate propeller rotation; and, (2) the blade control module then operates in the normal manner and drives the blades to obtain the selected pitch setting or angular velocity using battery power until the output of the alternator is sufficient to operate the propeller.
Reverse thrust capability is obtained by the following additions to the basic system for constant speed or variable pitch operation: (1) a blade pitch position sensor utilized to determine that the blades are in the reverse position or in the minimum pitch position for normal operation, wherein the blade position is fed back to the blade control module; (2) the reverse command is accomplished by a gate protected extended travel capability for the command sensor (alternatively an additional non-contact reverse sensor that is activated by the selection of reverse thrust may be utilized instead); (3) the blade control module would require additional logic to determine the state of the reverse sensor, wherein if the sensor is active, the blade control module activates the pitch changer to drive the blades to the reverse thrust position; and, (4) reverse thrust is obtained by setting the blade pitch to a specified position and modulating the reverse thrust and propeller angular velocity with throttle variation alone. It is also possible to govern the angular velocity by varying the propeller pitch within the available reverse thrust range. When governing is required, additional logic must be added to the blade control module to account for the operational sign change involved in reverse thrust operation.
Changing from reverse thrust operation back to normal operation is accomplished by returning the command sensor to the normal operating range and/or de-activating the reverse sensor. When the reverse sensor is no longer active, the blade control module will first command the pitch changer to move the blades to the normal operation minimum pitch setting and, if angular velocity is governed during reverse operation, cease the reverse governing function. When the minimum pitch setting for normal operation is achieved, the blade control module resumes normal operation. The system for activating reverse thrust must be suitably protected from inadvertent operation while in flight to prevent sensor commands for reverse thrust capability unless the airplane is on the ground.
Preferably, both feather and reverse capability is obtained by use of the gate protected extended travel of the command sensor. The gate protection for the feather operation can be a simple blocking device on the propeller control lever as is commonly utilized. Reverse operation requires a more complex gate, preferably in the form of an electromechanical device attached to the control module for blocking the sensor from the reverse position except when the appropriate ground operations are in progress. Common practice is to use a sensor on the landing gear that blocks reverse operation until there is sufficient weight on the wheels to assure the aircraft is on the ground.
Aircraft propellers specifically, and other applications are, in general good practice, designed so that any single failure of any portion of the system that controls the blade pitch will not result in an unsafe condition or a catastrophic failure. The current invention lends itself to the most fail safe remedies and warning systems.
Specifically, a complete loss of power due to the failure of the alternator or power control module may be remedied by one or more of the following: (1) counterbalanced blades to prevent the propeller blade pitch from moving to an unsafe position when power to the propeller is lost; and/or, (2) inclusion of a battery as a power backup or as required for feathering provides for normal operation to continue until the battery is exhausted, or for the blades to be set to a pre-selected pitch position, and the system shut down.
Complete failure of the blade control module may be remedied by the following: (1) redundant or multiple blade control modules to allow continued operation; and/or; (2) counterbalanced blades to prevent the propeller blade pitch from moving to an unsafe position when power to the propeller is lost.
Warning signals to the pilot or operator may be transmitted through additional non-contact sensors that are active when the system is operating normally.
Icing is always a problem with aircraft propellers as well. The various anti-icing or de-icing systems currently in use have the same problems as current variable pitch and constant speed propellers in that the power or other provisions for icing protection must be transferred from the fixed portion of the airframe or engine to the rotating propeller. The current invention lends itself to self-contained icing protection as a result of its self-contained power generation. Power for icing protection may be obtained by designing the alternator to provide sufficient power to both operate the propeller and provide electrical anti-icing or de-icing. Icing protection may be initiated automatically by the use of appropriate icing sensors or selected by the operator by means of an additional non contact sensor.
Accordingly, a feature and advantage of the present invention is its self-contained power and blade pitch control capability.
Another feature and advantage of the present invention is its ability to operate as a variable pitch propeller without having to directly transfer any form of power from the engine or gearbox to the propeller.
Another feature and advantage of the present invention is its ability to operate as a constant speed propeller without having to directly transfer any form of power from the engine or gearbox to the propeller.
Another feature and advantage of the present invention is its ability to operate as a fully feathering variable pitch propeller without having to directly transfer any form of power from the engine or gearbox to the propeller.
Another feature and advantage of the present invention is its ability to operate as a fully feathering constant speed propeller without having to directly transfer any form of power from the engine or gearbox to the propeller.
Another feature and advantage of the present invention is its ability to operate as a variable pitch propeller with reverse thrust capability without having to directly transfer any form of power from the engine or gearbox to the propeller.
Another feature and advantage of the present invention is its ability to operate as a constant speed propeller with reverse thrust capability without having to directly transfer any form of power from the engine or gearbox to the propeller.
Another feature and advantage of the present invention is its ability to operate as a fully feathering variable pitch propeller with reverse thrust capability without having to directly transfer any form of power from the engine or gearbox to the propeller.
Another feature and advantage of the present invention is its ability to operate as a fully feathering constant speed propeller with reverse thrust capability without having to directly transfer any form of power from the engine or gearbox to the propeller.
Another feature and advantage of the present invention is its applicability to many current propeller designs as well as future propeller design.
Another feature and advantage of the present invention is its wide applicability, as it is highly scalable and may therefore be applied to either very large propellers or very small propellers.
Another feature and advantage of the present invention is its applicability to devices other than aircraft propellers including, but not limited to, ventilation fans, wind machines, windmills, marine propellers, and other axial impellers.
Another feature and advantage of the present invention is its ability to precisely set the blade pitch angle of a variable pitch propeller.
Another feature and advantage of the present invention is its ability to precisely control angular velocity of a constant speed propeller.
Another feature and advantage of the present invention is its ability to control blade pitch or angular velocity via a non-contact sensor positionably adjustable by a simple manually-operated mechanical linkage.
Another feature and advantage of the present invention is its ability to control blade pitch or angular velocity via a non-contact sensor positionably adjustable by a simple automatically-operated mechanical linkage, such as those utilized in single power lever systems.
Another feature and advantage of the present invention is its ability to control blade pitch or angular velocity via a non-contact sensor positionably adjustable by a simple automatically-operated mechanical linkage, such as those utilized in variable flow ventilation systems and constant flow variable load air handling systems.
Another feature and advantage of the present invention is its incorporation of simple non-contact sensors to provide pilot warning of system component failures or inadequate performance.
Another feature and advantage of the present invention is its ability to provide propeller de-icing utilizing the self-contained electrical power generated via the present invention.
These and other objects, features and advantages of the present invention will become more apparent to one skilled in the art from the following description and claims when read in light of the accompanying drawings.